1. Field of the Invention
The present invention relates to a rotation angle detection apparatus, and more particularly relates to a rotation angle detection apparatus that is connected to a rotor such as a steering shaft of an automobile capable of generating two angle detection signals having 90 degree phase difference corresponding to the rotation angle and rotation direction of a steering wheel and capable of correctly detecting the rotation angle of the rotor by obtaining the cotangent angle of the obtained two angle detection signals.
2. Description of the Related Art
Generally, a rotation angle detection apparatus, which is an apparatus used for detecting the rotation angle of a rotor, is provided at least with a rotation angle detection unit for detecting the rotation angle of a rotor, a control unit for controlling the operation of the rotation angle detection apparatus, and a controller for controlling a controlled mechanism. In the case that a rotation angle detection apparatus is used for detecting the rotation angle of a steering shaft of an automobile, the rotation angle detection apparatus is mounted on an automobile, and a rotation angle detection unit is coupled with a steering shaft of the automobile. In this case, various types of rotation sensors have been used for a rotation angle detection unit in a rotation angle detection apparatus mounted on an automobile, a rotation sensor as described hereunder has been proposed as one of these various types of rotation sensors.
The above-mentioned proposed rotation sensor has a rotation angle detection unit provided with a base member and a rotor unit disposed rotatable with respect to the base member, and the rotor unit is coupled to a rotor, namely a steering shaft of an automobile in this case. Furthermore, the rotation angle detection unit has a first magnet and a second magnet disposed on the base member, a first Hall element and a second Hall element disposed on the rotor unit with approximately 90 degree interval at the position facing to the first magnet, and a third Hall element disposed at the position facing to the second magnet. When the rotor namely the rotor unit is rotated, the sine wave-like first angle detection signal and the second angle detection signal having the constant maximum amplitude, the same period, and 1/4 wavelength phase difference are generated, and a third angle detection signal having a period of the entire rotation range of the rotor unit that increases linearly is generated simultaneously from the third Hall element.
The generated first angle detection signal, the second angle detection signal, and the third angle detection signal are supplied to the control unit. The control unit detects the rough rotation angel and rotation direction with reference to the neutral position of the steering wheel (steering shaft) based on the supplied third angle detection signal. The control unit detects the fine rotation angle with reference to the neutral position of the steering wheel based on the supplied first angle detection signal and second angle detection signal. Then, the control unit supplies the rotation angle and rotation direction with reference to the neutral position of the steering wheel to the controller as the angle detection information. The controller finely performs suspension control and automatic transmission control of an automobile based on the supplied angle detection information.
Herein, FIG. 3 shows a characteristic diagram for describing the relation between the rotation angle of the steering wheel generated from the rotation sensor and the respective detection signal voltage values of the first to third angle detection signals in the rotation angle detection apparatus in which the above-mentioned proposed rotation sensor is used.
In FIG. 3, 16 represents the first angle detection signal, 17 represents the second angle detection signal, and 18 represents the third angle detection signal. These three signals represent the change of respective detection signal voltage values of the first to third angle detection signals 16, 17, and 18 for the entire rotation angle (xc2x1720 degrees with respect to the neutral position) of the steering wheel.
In this case, the first angle detection signal 16 and the second angle detection signal 17 are the same sine wave-like signals having the same maximum amplitude and the same one period, and having the 1/4 wavelength phase difference. The maximum voltage value is 4.5 V and the minimum voltage value is 0.5 V for both signals. The first angle detection signal 16 falls to the minimum value (voltage value of 0.5 V) at the rotation angles of xe2x88x9222.5 degrees and +67.5 degrees with respect to the neutral position, at the rotation angles of successive subtraction of xe2x88x9290 degrees from xe2x88x9222.5 degrees, and at the rotation angles of successive addition of +90 degrees to +6.75 degrees. The second angle detection signal 17 falls to the minimum value (voltage value of 0.5 V) at the rotation angle of the neutral position 0 degree, at the rotation angles of successive subtraction of xe2x88x9290 degrees from 0 degree, and at the rotation angle of successive addition of +90 degrees to 0 degree. On the other hand, the third detection signal 18 increases linearly from the rotation angle of xe2x88x92720 degrees to +720 degrees, and takes the minimum value (voltage value of 0.5 V) at the rotation angle of xe2x88x92720 degrees and takes the maximum value (voltage value of 4.5 V) at the rotation angle of +720 degrees.
FIG. 10 is a characteristic diagram that shows the enlarged range from the rotation angle of xe2x88x9290 degrees to +90 degrees of the characteristic diagram shown in FIG. 3.
In FIG. 10, 16U is an approximately linear upward (slope) portion of the first angle detection signal 16, 16D is an approximately linear downward (slope) portion of the first angle detection signal 16, 17U is an approximately linear upward (slope) portion of the second angle detection signal 17, and 17D is an approximately linear downward (slope) portion of the second angle detection signal 17. The same components shown in FIG. 10 as those shown in FIG. 3 are given the same characters.
The detection of the rotation angle and the rotation direction of the steering wheel executed by means of the known rotation angle detection apparatus will be described with reference to the characteristic diagram shown in FIG. 10.
At first, when the control unit detects the rotation direction with respect to the neutral position (rotation angle of 0 degree) of the steering wheel, the control unit uses the voltage value of the supplied third angle detection signal 18. In detail, if the voltage value of the third angle detection signal 18 is larger than 2.5 V, the control unit detects that the rotation direction of the steering wheel is the one direction (positive rotation angle direction) with respect to the neutral position, on the other hand if the voltage value of the third angle detection signal 18 is smaller than 2.5 V, the control unit detects that the rotation direction of the steering wheel is the other direction (negative rotation angle direction) with respect to the neutral position.
Next, the control unit divides the entire rotation angle xc2x1720 degrees of the steering wheel into rotation angle sections Nxe2x88x921, N, N+1, . . . . that are corresponding to each one wavelength of the first angle detection signal 16 and the second angle detection signal 17 as shown in FIG. 10, and detects the rough rotation angle that represents what rotation angle section corresponds to the rotation angle of the steering wheel depending on the voltage value of the supplied third angle detection signal 18. For example, when the control unit detects 2.8 V as the voltage value of the third angle detection signal 18, the control unit detects the angle section N as the angle section that is corresponding to that voltage value.
Next, the control unit determines the first voltage value V1 and the second voltage value V2 when the voltage value of the first angle detection signal 16 coincides with the voltage value of the second angle detection signal 17 in the detected angle section N. Then, the control unit specifies the first (second) angle detection signal 16 (17) located outside the range of the first voltage value V1 and the second voltage value V2, and specifies the first (second) angle detection signal 16 (17) located inside the range of the first voltage value V1 and the second voltage value V2 by use of the determined first voltage value V1 and the second voltage value V2.
Subsequently, the control unit determines whether the angle detection signal 16 (17) located inside the range of the first voltage value V1 and the second voltage value V2 is the first angle detection signal 16 or the second angle detection signal 17. Simultaneously, the control unit determines whether the first (second) angle detection signal 16 (17) located outside the range of the first voltage value V1 and the second voltage value V2 is smaller than the first voltage value V1 or larger than the second voltage value V2, and determines that the first (second) angle detection signal 16 (17) located inside the range of the first voltage value V1 and the second voltage value V2 is in which divided angle section out of the first divided angle section H1, the second divided angle section H2, the third divided angle section H3, and the fourth divided angle section H4, which have been formed by dividing one angle section N into four subsections.
As described hereinabove, by determining that the first (second) angle detection signal 16 (17) is in which divided angle section out of H1 to H4 in one angle section N, the control unit detects the fine rotation angle of the steering wheel.
Because in the conventional rotation angle detection apparatus the linear slope portions 16U, 16D, 17U, and 17D on the first angle section H1 to the fourth angle section H4 of the first and second angle detection signals 16 and 17 are used for detecting the fine rotation angle of the steering wheel, the detected value is discontinued at the switching point between the preceding linear slope portion (for example, 16U) and the subsequent linear portion (for example, 17U) when the detected fine rotation angle is switched from the one angle section (for example, the first angle section H1) to the next one angle section (for example, the second angle section H2).
In this case, if no rotation angle detection error is included in the preceding linear slope portion 16U and the subsequent linear slope portion 17U, then no error is included in the rotation angle detection value obtained by use of the preceding linear slope portion 16U and the subsequent linear slope portion 17U.
However, because the linear slope portion usually includes some rotation angle detection error though slightly, the rotation angle detection value fluctuates temporarily depending on the error direction of the rotation angle detection error when the preceding linear slope portion 16U is switched to the subsequent linear slope portion 17U.
A method for detecting the fine rotation angle of a steering wheel by use of the average amplitude value has been proposed by the applicant of the present invention in order to reduce such rotation angle detection value error that occurs in association with the conventional rotation angle detection apparatus. In this method, when the control unit detects the fine rotation angle by use of the first angle detection signal 16 and the second angle detection signal 17 generated from the rotation angle detection unit, the first area that locates in the range of 1/6 period around the center at the time point when the first (second) angle detection signal 16 (17) passes the average of the maximum value and the minimum value (in this case, the value obtained by subtracting the average value of the maximum value and the minimum value from the first (second) angle detection signal 16 (17) is defined to as the amplitude), the second area that locates in the range of 1/12 period of the first (second) angle detection signal 16 (17) outside the first area, and the third area that locates in the range of 1/12 period of the first (second) angle detection signal 16 (17) outside the second area are defined. To detect the fine rotation angle of the steering wheel, only the amplitude of the first (second) angle detection signal 16 (17) is used when the first (second) angle detection signal 16 (17) is in the first area, the amplitude obtained by averaging the amplitude of the first (second) angle detection signal 16 (17) and the amplitude of the second (first) angle detection signal 17 (16) in the ratio of 7:3 is used when the first (second) angle detection signal 16 (17) is in the second area, and the amplitude obtained by averaging the amplitude of the first (second) angle detection signal 16 (17) and the amplitude of the second (first) angle detection signal 17 (16) in the ratio 5:5 is used when the first (second) angle detection signal 16 (17) is in the third area.
According to the rotation angle detection apparatus described in the new proposal, even though the linear slope portions 16U and 16D of the first angle detection signal 16 and the linear slope portions 17U and 17D of the second angle detection signal 17 include slight rotation angle detection error, the rotation angle can be detected with smaller influence of the rotation angle detection error by use of the average amplitude values.
According to the rotation angle detection apparatus described in the new proposal, even though the linear slope portions 16U and 16D of the first angle detection signal 16 and/or the linear slope portions 17U and 17D of the second angle detection signal 17 include slight rotation angle detection error, the influence of the rotation angle detection error is reduced and the rotation angle is detected at high accuracy because the fine rotation angle of a steering wheel is detected by use of the average amplitude obtained by averaging the amplitude of the first angle detection signal 16 and the amplitude of the second angle detection signal 17 in the predetermined ratio near the switching area when the linear slope portion of the first (second) angle detection signal 16 (17) is switched to the linear slope portion of the second (first) angle detection signal 17 (16)
However, in the rotation angle detection apparatus described in the new proposal, though the rotation angle is detected by use of the average amplitude obtained by averaging the amplitude of the first angle detection signal 16 and the amplitude of the second angle detection signal 17 in the predetermined ratio, because the linear slope portions 16U and 16D of the first angle detection signal 16 and the linear slope portions 17U and 17D of the second angle detection signal 17 are used together with the amplitude of other portions, it is difficult to detect the rotation angle at higher accuracy, and it has been desired to develop an angle detection apparatus that is capable of detecting the rotation angle at higher accuracy.
The present invention has been accomplished in view of the technical background as described hereinabove, and it is an object of the present invention to provides a rotation angle detection apparatus that is capable of detecting the rotation angle at higher accuracy by detecting the rotation angle by use of the arctangent angle of the continuous amplitude ratio of the first and second angle detection signals.
To achieve the above-mentioned object, a rotation angle detection apparatus in accordance with the present invention comprises a rotor connected to a rotating body, a rotation angle detection unit for generating the first angle detection signal and the second angle detection signal of the sine waveform having a constant maximum amplitude and the same period and having approximately 1/4 wavelength phase difference concomitantly with the rotation of the rotor, a memory unit for storing the first angle detection signal and the second angle detection signal, and a control unit, wherein the control unit continuously detects the amplitude of the angle detection signal and the second angle detection signal, compares the detected amplitude absolute value of the first angle detection signal and amplitude absolute value of the second angle detection signal, determines the arctangent angle of the quotient value obtained by dividing the smaller amplitude absolute value by the larger amplitude absolute value to calculate the basic rotation angle of the rotating body, sets a plurality of angle processing cases based on the amplitude value of the first angle detection signal and/or the amplitude value of the second angle detection signal that have been calculated as described hereinabove, and converts the detected basic rotation angle to the different angle value according to the predetermined conversion equation for each of the plurality of angle processing cases that have been set as described hereinabove, and the rotation angle of the rotating body is thereby detected.
According to the above-mentioned structure, it is possible to use the continuous signal amplitude of the first angle detection signal and the second angle detection signal and to detect the rotation angle that is scarcely affected by the rotation angle detection error, and furthermore it is possible to detect the rotation angle with a high accuracy because the obtained oration angle value is converted to the corrected angle value that is suitable for the angle processing for each of angle processing cases.
In the rotation angle detection apparatus of the present invention, the rotation angle detection unit has two magnetic sensors facing to a magnet, and the two magnetic sensors generate the first angle detection signal and the second angle detection signal respectively concomitantly with rotation of the rotor.
Even though the output of the first angle detection signal and the second angle detection signal ark is reduced due to deterioration of the magnetic sensors, both magnetic sensors deteriorate similarly, the influence of the deterioration is offset, and as the result the arctangent value is scarcely affected because of the above-mentioned structure.
In the rotation angle detection apparatus in accordance with the present invention, it is preferable that the detected basic rotation angle is corrected by use of the correction value that is depending on the attached position error value of the two magnetic sensors.
Because the angle error due to the attached position error of the two magnetic sensors is eliminated from the angle value that has been converted according to the predetermined conversion equation set for each of a plurality of angle processing cases, the sine wave error string having a period corresponding to the attached position error of the two magnetic sensors included in the basic rotation angle is reduced significantly. As the result, it is made possible to detect the rotation angle with a higher accuracy.
Furthermore, in the rotation angle detection apparatus in accordance with the present invention, it is preferable that the angle processing case is set depending on the polarity, namely positive polarity or negative polarity, of each amplitude and the magnitude of the amplitude absolute value of the amplitude in the case that the first angle detection signal and the second angle detection signal are both used.
According to the above-mentioned structure, the rotation angle is detected with a high accuracy.
Furthermore, in the rotation angle detection apparatus in accordance with the present invention, it is preferable that the set angle processing case is selected so that; the arctangent angle is set as the rotation angle when the amplitude value of the first angle detection signal is equal to or larger than zero, the amplitude absolute value of the first angle detection signal is equal to or smaller than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is smaller than zero; the value obtained by subtracting the arctangent angle from 180 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is equal to or larger than zero, the amplitude absolute value of the first angle detection signal is equal to or smaller than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is equal to or larger than zero; the value obtained by adding the arctangent angle to 90 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is equal to or larger than zero, the amplitude absolute value of the first angle detection signal is larger than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is equal to or larger than zero; the value obtained by subtracting the arctangent angle from 90 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is equal to or larger than zero, the amplitude absolute value of the first angle detection signal is larger than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is smaller than zero; the value obtained by subtracting the arctangent angle from 270 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is smaller than zero, the amplitude absolute value of the first angle detection signal is equal to or larger than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is equal to or larger than zero; the value obtained by adding the arctangent angle to 270 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is smaller than zero, the amplitude absolute value of the first angle detection signal is equal to or larger than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is smaller than zero; the value obtained by adding the arctangent angle to 180 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is smaller than zero, the amplitude absolute value of the first angle detection signal is smaller than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is equal to or larger than zero; and the value obtained by subtracting the arctangent angle from 360 degrees is set as the rotation angle when the amplitude value of the first angle detection signal is smaller than zero, the amplitude absolute value of the first angle detection signal is smaller than the amplitude absolute value of the second angle detection signal, and the amplitude value of the second angle detection signal is smaller than zero.
By applying the above-mentioned structure, the rotation error is detected reliably with a high accuracy regardless of the magnitude of the rotation angle.
In the rotation angle detection apparatus in accordance with the present invention, it is more preferable that the rotating body is a steering shaft of an automobile, and the rotation angle signal calculated from the first angle detection signal and second angle detection signal is a steering angle signal of the steering shaft.
By applying the above-mentioned structure, the rotation angle of a steering shaft of an automobile is detected with high accuracy.
In the rotation angle detection apparatus in accordance with the present invention, it is preferable that the steering angle detection signal is supplied to a controller through a local area network bus line installed in the automobile.
Thereby, the suspension and the automatic transmission mechanism are controlled properly based on the rotation angle of the steering shaft of the automobile.